One of the following is NOT part of the integumentary system. Which one?

Correct Answer: A

Rationale: The integumentary system includes the skin (epidermis and dermis), hair, nails, and glands like sebaceous glands. The hypodermis, or subcutaneous layer, lies beneath the dermis and isn't considered part of the integument proper, despite its adjacency. Sebaceous glands in the dermis, fingernails (epidermal derivatives), and the stratum corneum (epidermis) are all integumentary components. The hypodermis's exclusion, as superficial fascia, is a consistent anatomical distinction, making it the odd one out.

Correct Answer: A

Rationale: Sudiferous glands (sweat glands) produce sweat, either watery (eccrine) or thicker (apocrine), for thermoregulation and excretion. Sebum is from sebaceous glands, cerumin (cerumen) from ceruminous glands, and 'merocrin' is a typo or misnomer (merocrine describes eccrine secretion mode, not a substance). Sweat's role as the sudiferous output, distinct from other glandular products, confirms it as the correct secretion.

Correct Answer: A

Rationale: Sweat glands, primarily eccrine, regulate body temperature by secreting sweat, which evaporates to cool the skin, a key thermoregulatory mechanism. Melanin production is melanocytes' job, not glands'. Hair follicle nourishment involves blood vessels and sebum, not sweat. Joint lubrication is synovial fluid's role, not skin-related. Sweat glands' production of water and electrolytes, triggered by heat or exercise, directly supports homeostasis by dissipating heat, making temperature regulation their primary function, widely recognized in physiology.

Correct Answer: C

Rationale: Melanocytes, in the stratum basale, produce melanin pigment, which colors skin and protects against UV radiation by absorbing it, reducing DNA damage. Temperature regulation involves sweat glands and vessels, not melanocytes. Sweat is from sudiferous glands, not pigment cells. Hair follicle nourishment comes from dermal blood and sebum, not melanocytes. Melanin's role in pigmentation and photoprotection, distributed to keratinocytes, defines their primary function, a vital epidermal process.

Correct Answer: D

Rationale: Vitamin D synthesis occurs in the skin when UV light converts 7-dehydrocholesterol in the epidermis to previtamin D3, essential for calcium absorption. Thermoregulation uses sweat and vessels, sensation involves receptors, and excretion removes waste via sweat, none involving UV-driven synthesis. This photochemical process, unique to skin, distinguishes vitamin D production as a key function, making it the correct answer.